Tobacco and other herbs are typically smoked by burning and inhaling the combustion fumes and smoke. In recent years, interest has grown in the technique of vaporization in which the smoking material is carefully heated so that the desired flavor and psychoactive components are liberated, and combustion is minimized.
Vaporization provides many benefits over smoking. Vaporization produces much less toxic and carcinogenic pyrolytic products compared to smoking. Also, vaporization is smoother and more flavorful, and lacks the disagreeable burned taste produced by conventional smoking. Further, vaporization allows more efficient use of smoking materials, since desired flavor and psychoactive compounds are not destroyed by combustion.
However, vaporization is difficult to perform, since vaporization only occurs in a relatively narrow temperature range. If the temperature is too low, desired compounds are not vaporized and nothing is inhaled; if the temperature is too high, combustion will occur. For most smoking materials, vaporization is optimal in a temperature range of about 300-400 degrees Fahrenheit. The optimal temperature depends upon the compounds being vaporized.
U.S. Pat. No. 7,434,584 teaches a portable and effective vaporization pipe that has found significant market success. The top filter unit of this pipe presents some manufacturing difficulties that are explained in reference to FIG. 1. A filter housing 10 is made of wood. A porous ceramic foam filter element 12 and eyelet 13 are disposed in the filter housing. A male threaded ring 14 is tightly screwed into the wood housing 10. A few turns of the threaded ring are exposed for attachment to a female-threaded bowl (not shown). This design is cost effective and functional, but it has several problems:
1) The filter housing must have threads cut into the wood. The thread cutting process is slow and labor-intensive. Also, thread cutting causes chipping and damage to the wood edges.
2) Thread cutting requires the wood fibers to be oriented perpendicular to the central hole (i.e. in a horizontal/transverse direction). This increases the cost of the filter housing, and increases the difficulty of fabricating the filter housing part. Also, wood parts with this unusual wood fiber orientation are more difficult to finish and have a less attractive finished appearance.3) The process of inserting the threaded ring and screwing it tightly is slow and labor intensive, and tends to damage the wood parts.4) The tightly screwed threaded tube tends to cause the filter housing to crack and split, because the tube produces a large outward force on the inside surface of the filter housing. This reduces the reliability and durability of the product, and increases warranty replacement costs.
Accordingly there is a need for an improved filter unit design that is easier and faster to manufacture, and that has a lower defect rate.